Process for forming a lithium-calcium grease composition



United States Patent O PROCESS FOR FORMING A LITHIUM-CALCIUM GREASE COMPOSITION Rosemary OHalloran, Union, and Hans G. Vesterdal, Elizabeth, N.J., and Alan Beerbower, Baltimore, Md., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Nov. 25, 1955, Ser. No. 549,195 A 3 Claims. (Cl. 252-40) This invention relates to lubricating grease compositions and to a process for their manufacture. Particularly, the invention relates to a process for the preparation of lubricating grease compositions containing lithium and calcium soaps of high molecular weight fatty acids in a range of molar ratios of from 2:1 to 8:1 mols of lithium soap to mols of calcium soap.

This application is a continuation-in-part of Serial No. 477,174, filed December 23, 1954, of similar inventorship and which has been abandoned.

Lithium-calcium soap greases are known to the art. U.S. Patents 2,641,577 and 2,646,401 describe in detail the composition and preparation of improved lubricating greases of this type. These greases are prepared conventionally by saponification, dehydration, addition of oil at about 300 F., cooking until the mixture is es: sentially liquid, that is, to about 350 to 450 F. and pan cooling without agitation to ambient temperatures, or temperatures below the transition temperature of the soap thickener. The cooled grease is then mashed down to the desired consistency and packaged. A conventional lithium calcium grease composition and its method of preparation is as follows:

Formulation Weight Percent Cottonseed Fatty Acids Lithium Hydroxide Monohydraten Hydrated Lime (71% Ca). Mineral Oil (500 SUS/100 F.)

2,959,548 Patented Nov. 8, 1960 ice is then subjected to high rates of shear in excess of about 100,000, preferably about 200,000 to 600,000, reciprocal seconds in a suitable milling or homogenizing device to increase the yield and make a more stable product. However, even without milling, a smooth grease of good appearance is obtained. The temperature to which the grease is cooled before milling depends on the type of milling equipment used and the temperature rise caused by the milling treatment. In general, this temperature should be such as will permit the grease to leave the milling device at a temperature below 200 F. The temperature rise in the milling device is a direct function of wheel bearing lubricating service when animal fatty acids.

are employed as the saponifiable thickening ingredients. More specifically, it has been discovered that the use of animal fatty acids having an iodine number of from about 40 to 60 is critical with respect to the preparation of a lithium-calcium base grease which will not soften or leak excessively when utilized under actual performance conditions involving elevated temperature and vibratory conditions. Animal fatty acids having from about 12 to 22 carbon atoms per molecule such as those derived from beef tallow, mutton tallow, goat tallow, lard, etc. are especially suitable for the purposes of this invention. It is possible, of course, to use the animal fat having an iodine number within the above range directly in the manufacture of the inventive lubricating grease compositions.

The mol ratio of the lithium and calcium soaps em-. ployed as the thickeners of this invention may vary from. about 2 mols of lithium soap to about 1 mol of calcium.

soap, to about 8 mols of lithium soap to about 1 mol of calcium soap. A preferred range is a mol ratio of lithium soap to calcium soap of from 2: 1 to 6: 1.

Though the total soap concentration in the lubricating grease compositions of this inventionmay be within the range of about 9 to 50 wt. percent, preferable concenwhich time the remainder of the oil is added in small amounts. The temperature is again raised to about 350365 F. until the product is completely fluid. The product is then pan cooled to room temperature. The cooling step occupies from about 8 to about 24 hours. The grease cakes are then stirred down and filtered.

It has now been found that the expensive and timeconsuming pan cooling and stir-down steps can be eliminated and grease compositions formed at substantially lower kettle temperatures. In accordance with the invention, the grease is dehydrated in the form of a concentrate at temperatures not exceeding that obtainable in ordinary steam kettles. Thus, the grease may be dehydrated at a temperature as low as 220 F., the preferred dehydration temperature range being about 260- 320 F. In order to obtain the lubricating grease compositions of this invention, the dehydration must be carried out without melting the soap thickeners.

' Following dehydration the grease concentrate is cooled, preferably by the addition of cold oil under stirring, to a temperature of about 100-200 F. The cooled grease etc.), esters of phosphoric acid (e.g. the ester formed trations are about 12 to 30 wt. percent, based on the total lubricating grease composition. As hereinafter shown, the amount of soap employed is an important feature of this invention. The excess free alkalinity of the finished grease will be maintatined between about 0.1 and 1.0%, calculated as sodium hydroxide, to assure good storage stability.

The lubricating oil base stock employed in this invention may be any of mineral or synthetic lubricating oils known to the art. In general, these lubricating oilsshould have a viscosity of about 50 to 2000 S.U.S. at 100 F. and about 35 to 200 S.U.S. at 210 F. an ASTM pour point of about +20 to F., a flash point of about 350 to 650 F., and a viscosity index of about 0 to 60. Conventionally refined mineral oil base stocks from paraffinic or naphthenic crude sources having the;

properties listed above may be used.

The synthetic lubricating oils include esters of monobasic acids (e.g. an ester of C Oxo alcohol with C 0x0 acid, an ester of C Oxo alcohol with octanoic acid,

etc.), esters of dibasic acids (e.g. di-Z-ethyl hexyl seba-" formed by reacting one mole of tetraethylene glycol, one.

mole of C Qxo alcohol and one mole of C 0x0 acid,

by contacting three moles of the mono-methyl ether of ethylene glycol with one mole of phosphorous oxychloride, etc.), halocarbon oils (e.g. the polymer of chlorotrifluoroethylene containing twelve recurring units of chlorotrifluoroethylene), alkyl silicates (e.g. methyl polysiloxanes, ethyl polysiloxanes, methyl-phenyl polysiloxanes, etc.), sulfite esters (e.g. ester formed by reacting one mole of sulfur oxychloride with two moles of themethyl ether of ethylene glycol, etc.), carbonates (e.g. the carbonate formed by reacting C Oxo alcohol with ethyl carbonate to form a half ester and reacting this half ester with tetraethylene glycol), mercaptals (e.g. themercaptal formed by reacting Z-ethyl. hexyl mercaptan with formaldehyde), formals (e.g. the formal formed by reacting C Oxo alcohol with formaldehyde), polyglycol type synthetic oils (e.g. the compounds formed by condensing butyl alcohol with fourteen units of propylene oxide, etc.), or mixtures of the above in any proportions.

The lubricating grease compositions of the invention will contain about 50 to 91 wt. percent, preferably 70 to 88 Wt. percent, of the mineral and/or synthetic lubricating oils.

It is also within the scope of the invention to add any of the conventional additives to the present lubricating grease compositions. Oxidation inhibitors, such as phenyl alpha naphthylamine, rust and corrosion inhibitors, metal deactivators, extreme pressure agents, and the like may be added, usually after dehydration and along with the addition of the remainder of the lubricating oil.

The preferred method of preparing the lubricating grease compositions of the invention involves charging the fatty acid and a portion of the lubricating oil, e.g. about /s% of the total oil, to a steam-heated grease kettle. The temperature of the kettle may then be gradually raised to about l30-170 F. and the hydrated lime-calcium hydroxide-added. Stirring is commenced and the temperature may be gradually raised while the lithium hydroxide is added. However, if desired, the hydrated lime and the lithium hydroxide may be added before heating is started. The grease is heated until the grease is practically dehydrated at a temperature of 260-3l0 R, which is substantially below the melting point of the grease formed. Then the heat is shut off and the balance of cold oil may be added in incremental amounts at this point or the soap concentrate may first be cooled to a temperature of about 180 200 F. before adding the balance of the oil.

The mixture may then be subjected to the action of high rates of shear in a milling device, such as Morehouse mill, a Charlotte mill, ink mill, Gaulin homogenizer, three-roll paint mill or similar device, entering the mill at a temperature of, say, about 100-l50 F. to be heated by the milling action to a temperature not exceeding 200 F.

Rather than adding all the fatty acids initially, it may be desirable to charge first only enough of the fatty acids to neutralize the lime and after neutralization, add the lithium hydroxide solution and. the remainder of the fatty acids. Also, the lithium hydroxide maybe added. to the charge prior to the lime.

The invention will be further illustrated by the follow ing specific examples.

EXAMPLE I Formulations 1 Commercial acid from hydrolyzed tallow having an iodine number about 40 and a saponification number of about 200.-

I Iodine number about 100;

Preparation Greases A to C were prepared substantially in the same manner as follows. The fatty acid and about /2 of the mineral oil were added to the steam kettle and the calcium hydroxide powder was stirred in at the temperatures listed below. Heating and stirring were continued and the lithium hydroxide was added as a 10% aqueous solution at the temperatures given below. The greases were then further heated to the end temperatures given below to dehydration. During this period, the viscosity of the mass was cut down by the addition of small amounts of oil. Thereafter the heat was shut off and the balance of the cold oil was added while stirring, over a period of about 1-2 hours. None of the greases were melted dur- Following the addition of all of the oil, the above greases were passed through a Morehouse mill at a stone clearance of about and at the following temperatures:

Inlet temperature, F

Outlet temperature, F

Properties A B 0 Smooth...

Appearance Grainy. Penetration (77 F., mm./l0):

Unwcrked Worked (60 strokes) Worked (60,000 strokes)- Penetration (210 F., mm./1 Dropping Point, F.. String Length, Inches 1 OllSeparation (50 hrs. 210

F.) Percent. Regular Wheel Bearing Test Leakage, grams Accelerated Wheel Bearing Test.

Leakage, grams 0. 5 Field Test Pertormance Excellent.

19. 5. Failure.

8. 5 Borderline.

l lgleti iod otdetermlning string length is described in U.S. Patent No.

64 .40 I This grease is of possible use in passenger cars, but ineffective in truck lubricating services.

The regular wheel bearing test involves placing a sample of the grease in a standard Ford wheel bearing, and spinning the bearing at 660 r.p.m. for six hours at a temperature of 220 F. If any of the sample slumps or ten grams of oil leak from the bearing after the test period, the' grcase is rated as having failed the test.

In the accelerated test the wheel bearing assembly is tilted 15 degrees towards the shield. With a regular charge of 90 grams of the grease in the bearings and hub, the motor is started and both heaters are left on until the spindle temperature has been raised to about 200 F. (about 20 minutes) and the oven temperature to about 235 F. An electric vibrator attached to the back of the oven next to the spindle support bolts is then started and left on for one hour. The spindle temperature is then about 215 to 220 F. The amount of grease slumped into the shield is weighed to determine whether the grease has passed or failed this test.

The accelerated wheel hearing test is considered to be better than the regular wheel bearing test, since the latter test does appear to be severe enough to clearly distinguish between an acceptable grease and an outstanding grease.

The accelerated wheel hearing test is also considered to give a more accurate determination of the greases capabilities under particular operating conditions such as hot weather. The superiority of this test to the regular wheel bearing test is clearly indicated by the above data, which show that whereas greases B and C had passing ratings in the regular test and showed very little leakage, they did not pass the accelerated test since they showed both slumping and heavy leakage. The latter determinations were substantiated by actual-'field' test results.

The above data also show that grease A, prepared from animal fatty acids in the percentages and by the method of this invention, was superior to greases prepared from cottonseed fatty acids '(greasef C) for from animal fatty acids wherein the total soap content is less than the prescribed 9 wt. percent (grease B). It will be noted that grease A had a higher dropping point, a more desirable consistency at 210 F., less oil separation, etc. than greases B and C. It should be particularly noted that grease A showed considerably less leakage in the accelerated wheel bearing test than either of the other greases, indicating its superiority for lubricating services involving severe operating conditions.

1 Commercial acids from hydrolyzed tallow having an iodine number of about 40 and a saponifieation number of about 200.

Procedure The acids were diluted with an about equal weight of the mineral oil and the calcium hydroxide was added thereto as an oil slurry at about 130 F. After about 15 minutes of stirring, the lithium hydroxide was added as an aqueous solution of about 10% LiOH concentration. The soap concentrate was then heated to about 310 F. to dehydration. The heat was turned off and the remainder of the (cold) oil was added slowly over a period of about 1 hour to cool until the grease had reached a temperature of about 175 F. At this point part of the grease was milled in a Charlotte mill at a clearance of A The temperature of the grease rose to 207 F. due to milling. The milled grease was grainy, even more so than the grease before milling, which was fairly smooth.

The rest of the unmilled grease was cooled further to 140 F. before milling and then was milled at the same stone clearance as before. The temperature in this case rose to 190 F. due to milling. The milled grease was smooth and stayed smooth permanently. These experiments demonstrate the importance of maintaining the mill out-let temperature of the grease below about 200 F.

1 Commercial acids from hydrolyzed tallow having an iodine number of about 40 and a saponification number of about 200.

Procedure The lime was dispersed in about /2 of the mineral oil and the fatty acids were added to this mixture at room temperature. The mass was heated while stirring to about 150 F. and the lithium hydroxide was added as a 10% aqueous solution. This mixture was passed through a laboratory Morehouse mill at about ,4 clearance. The milled soap concentrate was placed in pans in V4" layers and dehydrated in a forced draft oven overnight at 223 F. The remaining /2 of the oil was heated to 220 F. and mixed with the now dehydrated soap con: centrate in a Hobart mixer. The grease was allowed to cool down to about F. while mixing and then was milled twice in the laboratory Morehouse mill at M clearance.

The unworked penetration of the grease was 280. The appearance of the grease was satisfactory. I

'The aboveexample illustrates the fact that excellent greases may be'made in accordance with the invention at cooking temperatures below 250 F. and substantially below the melting point of the greases, which lies normally in the neighborhood of about 350 F.

EXAMPLE IV The following example demonstates the utility of the invention for the preparation of synthetic oil base greases.

Procedure The lime was dispersed in about V2 the ester and the fatty acids were mixed in at room temperature. This mixture was added to a boiling 10% aqueous lithium hydroxide solution and stirred smooth. Thereafter, the soap concentrate was dehydrated on a low-heat hot plate by heating to 315 F. The heat was removed and the rest of the ester was stirred in slowly, thereby reducing the grease temperature to about 230 F. After further cooling below 200 F., the grease was passed twice through a laboratory Morehouse mill at a clearance of ig A soft smooth grease having an unworked penetration of 330 was obtained.

The low cooking temperature of the present invention is particularly advantageous for synthetic ester oils of this type because ester losses by evaporation of light ends and heat degradation of the ester are minimized. As a result, improved low temperature properties are obtained.

In brief summary, this invention involves preparing lithium-calcium base greases by employing animal fatty acids having an iodine number from about 40 to 60 as the saponifiable grease-thickening material, and by utilizing the low temperature steam kett-le process outlined above. It is also essential that the milling step be accomplished at temperatures below about 200 F. If the grease compositions are milled with an outlet temperature above about 200 F., the crystalline formation of the grease miscelles is accentuated and the resulting composition will be undesirably grainy.

It will be further understood that the present invention is not necessarily limited to the specific materials and conditions of the foregoing examples. These materials and conditions may be varied within the limits indicated in the general portions of the specification.

What is claimed is:

1. A method of preparing an improved lubricating grease composition which comprises a major amount of a lubricating oil and 9 to 50 wt. percent of a mixture of lithium and calcium soaps of C to C fatty acids wherein the mol ratio of said lithium soap to said calcium soap is within the range of 2:1 to 8:1, which comprises dispersing in said lubricating oil an animal fatty acid containing 12 to 22 carbon atoms per molecule and having an iodine number about 40to 60, adding lithium and calcium bases to said dispersion, heating to a temperature within the range of 260 to 320 F. and below the melting temperature of said soaps to saponify said acids and dehydrate the mixture, cooling to a temperature below 200 F. and then homogenizing the composition at a rate of shear in the range of about 100,000 to 600,000 reciprocal seconds.

2. A process according to claim 1 wherein said lubrieating grease composition comprises a mineral lubricating oil, 12 to 30 Wt. percent of said lithium and calcium soap and wherein said lithium and calcium bases are lithium hydroxide and calcium hydroxide.

3. A process according to claim 1 wherein said animal fatty acids have an iodine number of about 40 and are obtained by hydrolyzing tallow.

References Cited in the file of this patent UNITED STATES PATENTS 2,444,720 Bell July 6, 1948 2,641,577 O?Halloran June 9, 1953 2,652,366 Jones et a1. Sept. 15, 1953 2,704,363 Armstrong Mar. 15, 1955 2,824,064 Musselman ct a1. Feb. 18, 1958 OTHER REFERENCES Manufacture and Application of Lubricating Greases, Bonner, Reinhold Pub. Corp., NY. (.1954), p. 134. 

1. A METHOD OF PREPARING AN IMPROVED LUBRICATING GREASE COMPOSITION WHICH COMPRISES A MAJOR AMOUNT OF A LUBRICATING OIL AND 9 TO 50 WT. PERCENT OF A MIXTURE OF LITHIUM AND CALCIUM SOAPS OF C12 TO C22 FATTY ACIDS WHEREIN THE MOL RATIO OF SAID LITHIUM SOAP TO SAID CALCIUM SOAP IS WITHIN THE RANGE OF 2:1 TO 8:1, WHICH COMPRISES DISPERSING IN SAID LUBRICATING OIL AN ANIMAL FATTY ACID CONTAINING 12 TO 22 CARBON ATOMS PER MOLECULE AND HAVING AN IODINE NUMBER ABOUT 40 TO 60, ADDING LITHIUM AND CALCIUM BASE TO SAID DISPERSION, HEATING TO A TEMPPERATURE WITHIN THE RANGE OF 260* TO 320*F. AND BELOW THE MELTING TEMPERATURE OF SAID SOAPS OF SAPONIFY SAID ACIDS AND DEHYDRATE THE MIXTURE, COOLING TO A TEMPERATURE BELOW 200*F. AND THEN HOMOGENIZING THE COMPOSITION AT A RATE OF SHEAR IN THE RANGE OF ABOUT 100,000 TO 600,000 RECIPROCAL SECONDS. 